1. Field of the Invention
The present invention relates generally to fuel supply systems for providing compressed natural gas fuel to a transit bus or the like.
2. Description of the Prior Art
As the search continues for cleaner burning fuels to reduce pollution in the nation""s cities, many city transit authorities are converting their bus fleets to run on compressed natural gas, commonly referred to as CNG.
Due to the high pressures at which the CNG must be stored, this presents unique engineering challenges for construction of the fuel systems.
Typically, the fuel on a CNG powered bus is stored in a series of elongated cylindrical tanks. These tanks may either be mounted below the floor of the bus or on top of the roof of the bus.
One example of a prior art roof mounted CNG fuel system for a transit bus is that manufactured by New Flyer. The New Flyer system utilizes a combination of four forward mounted and three rearward mounted Type 4 tank cylinders mounted on top of the bus. Type 4 tanks utilize a plastic liner with a carbon fiber overwrap. The tanks are supported by a pair of saddles and strap assemblies which typically support the tank at approximately xc2xc the distance from either end of the tank.
The New Flyer tanks are each supported on top of the bus by two saddles which are located immediately below their respective tanks. Two transverse manifold lines run across the roof of the bus between the forward and rearward tanks. Each tank includes a solenoid valve mounted in its end adjacent the tank, and a single piece of tubing connects each tank to one of the manifold lines, with the tank being both filled and discharged through that single piece of tubing. The tubing includes a horizontal portion, a 90xc2x0 upward bend, a vertical portion, a 90xc2x0 bend, a horizontal portion, another 90xc2x0 bend and then a vertical portion extending downward into a lateral port in the solenoid valve structure.
There are some shortcomings of prior art systems like that of New Flyer. One shortcoming is due to the mounting of the solenoid directly in the end of the tank. If the solenoid needs servicing, the entire tank must be emptied and purged so that the solenoid can be removed.
Another shortcoming is the inadequacy of flexibility provided in the connecting conduit which can place excessive strain on the manifold line when the tank expands due to thermal expansion.
Another prior art roof mounted CNG fuel supply system for transit buses is that in use by Orion Bus Industries. The Orion system includes four forward and four rearward roof mounted tank cylinders. The Orion tanks are Type 3 tanks. Type 3 tanks utilized an aluminum liner wrapped with a carbon fiber wrap. Type 3 tanks are mounted at their xe2x80x9cneckxe2x80x9d which is the end adjacent the manifold line. Substantially all thermal expansion of a Type 3 tank occurs at the end opposite the manifold line, thus flexing of the conduits connecting the manifold line to the tank are not a significant issue when utilizing Type 3 tanks.
The Orion system utilizes two parallel manifold lines which are not anchored to the bus, but which rather are supported from the tanks themselves. Thus, there is no longitudinal movement of the tank relative to the manifold line. The Orion tanks include a manual shutoff valve mounted in the end of the tank. A check valve is mounted on one side of the shutoff valve and a solenoid valve is mounted on the other side of the shutoff valve. An S-shaped tube connects the manifold line to the check valve. A return tube connects the solenoid valve to the manifold line. To the extent there is flexibility built into the tubing lines of the Orion system, it is provided simply to accommodate flexing of the bus itself, and not because of any thermal expansion of the tank end relative to the manifold line.
Thus, it is seen that there is a need for improvement in CNG fuel supply systems, and particularly for improvement in the design and construction of the manifold lines and tubing connecting the manifold lines to the tanks when utilizing Type 4 tanks which exhibit substantial thermal expansion relative to the manifold lines.
The present invention provides a CNG fuel supply system for a bus, the bus having a top and having a length and a width. The system includes a plurality of forward tank cylinders mounted on the top of the bus and extending parallel to the length of the bus, and a plurality of rearward tank cylinders. A CNG manifold line has a length extending transversely across the bus between the forward tank cylinders and the rearward tank cylinders. The CNG manifold line is anchored so that it does not move relative to the length of the bus. A plurality of inlet lines connect the manifold line to the tank cylinders, said plurality of inlet lines including a plurality of bendable inlet expansion portions, one of which is associated with each tank cylinder for accommodating longitudinal expansion of the tank cylinder. The system also includes a plurality of outlet lines connecting the tank cylinders to the manifold line, said plurality of outlet lines including a plurality of bendable outlet expansion portions, one of which is associated with each tank cylinder for accommodating longitudinal expansion of the tank cylinder.
The bendable inlet and outlet expansion portions preferably include a continuous 180xc2x0 bend having a radius of at least 1xc2xd inches which can accommodate xc2xe inch longitudinal movement of the tank cylinder relative to the manifold line.
A plurality of check valves are associated with the inlet lines for allowing flow of CNG from the manifold line through the inlet lines to the tank cylinders while preventing flow in the opposite direction. In one embodiment, each check valve is associated with two of the inlet lines for controlling flow of CNG from the manifold line to two of the tank cylinders.
A plurality of solenoid valves are associated with the outlet lines for controlling flow of CNG from the tank cylinders through the outlet lines to the manifold line. In one embodiment, one of the solenoid valves is associated with two of the outlet lines for controlling flow of CNG from two of the tank cylinders to the manifold line.
Each tank cylinder has a manual shutoff valve mounted in an end thereof adjacent the manifold line. The shut off valve can be closed to isolate the tank from the solenoid valve, check valve and inlet and outlet tubing. Each of the solenoid valves is removably mounted in its respective outlet line so that the solenoid valve may be removed and replaced without having to empty and purge its associated tank cylinder.
Each of the inlet and outlet lines are constructed from machine bent tubing pre-fabricated to specified tolerances so that pre-fabricated replacement parts may be substituted for original parts to repair the system.
Preferably, the system is designed so that many of the inlet and outlet lines for both the forward and rearward groups of tank cylinders are interchangeable so as to reduce the number of pre-fabricated components which must be kept in inventory for maintenance purposes.
In one embodiment, the inlet lines for two adjacent tank cylinders include a common line portion connected to the manifold line and having the check valve disposed therein. A T is connected to the first line portion and then first and second hydraulically parallel separate line portions separately connect the T to the first and second tanks. These separate line portions include the flexible inlet expansion portions.
In another embodiment, the fuel system is designed to be originally constructed utilizing two forward tanks and four rearward tanks, and to be subsequently modified to include two additional forward tanks. The inlet and outlet tubing for the two original forward tanks is constructed so that it may be replaced with inlet and outlet tubing identical to the rearward tank group.
It is, therefore, an object of the present invention to provide an improved CNG fuel supply system for a bus.
Another object of the present invention is the provision of a CNG fuel supply system which may be utilized with a fleet of buses and which utilizes interchangeable machine bent pre-fabricated tubing sections, which are interchangeable between buses, and which may be provided from inventory for replacement purposes to repair a bus.
Another object of the present invention is the provision of a CNG fuel supply system having increased safety due to the provision of improved expansion loops in the connecting tubing to accommodate thermal expansion of a Type 4 tank.
Still another object of the present invention is the provision of a CNG fuel supply system which utilizes solenoid valves which may be removed from their respective tanks without having to empty and purge the tank.
Other and further objects, features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the following disclosure when taken in conjunction with the accompanying drawings.